docs: def get_biopython_pepstats(self, clean_seq=False):
          """Run Biopython's built in ProteinAnalysis module and store statistics in the ``annotations`` attribute."""
  
          if self.seq:
              if clean_seq:  # TODO: can make this a property of the SeqProp class
                  seq = self.seq_str.replace('X', '').replace('U', '')
              else:
                  seq = self.seq_str
  
              try:
                  pepstats = ssbio.protein.sequence.properties.residues.biopython_protein_analysis(seq)
              except KeyError as e:
                  log.error('{}: unable to run ProteinAnalysis module, unknown amino acid {}'.format(self.id, e))
                  return
              except ValueError as e:
                  log.error('{}: unable to run ProteinAnalysis module, {}'.format(self.id, e))
                  return
              self.annotations.update(pepstats)
          else:
              raise ValueError('{}: no sequence available, unable to run ProteinAnalysis'.format(self.id))